The present invention relates to an automative engine oil deterioration monitoring system and more particularly provides an automative system to monitor engine oil which is capable of predicting the time, in the future, when the engine oil should be changed.
Hochstein U.S. Pat. No. 4,007,629 discloses a method and apparatus for monitoring oil degradation. The system incorporates an intricate mechanical structure which is subject to mechanical failure. However, according to this patent an alarm signal is provided only when the oil has already deteriorated to an undesirable level. It is more desirable for a driver to know in advance when he should change the engine oil by continuously monitoring the change in oil deterioration and determining the remaining useful life of the oil.
Unlike the above patented system, the present invention does not measure the oil deterioration directly but provides a system to continuously estimate the change in oil deterioration based on the oil temperature history or engine RPM history. The present invention, therefore, estimates the remaining time or mileage before the oil will reach an undesirable deterioration level.
There are various causes of oil deterioration. It has been discovered in accordance with the present invention, however, that engine oil temperature, engine running time and the time elapsed from the previous oil change are important parameters to estimate the degree of deterioration with respect to the following major causes of oil deterioration. First, oxidation of engine oil is one of the major causes of oil deterioration and the degree of oxidation is a function of temperature and time. If the temperature is high, the oxidation progresses faster and if the reaction time at a certain temperature is longer, more oxidation occurs. Second, oil molecules are broken by mechanical action, such as friction, between a piston and a cylinder. These molecular breaks produce sludge and decrease lubricity. This mechanical damage occurs more readily when the viscosity of the oil is low due to low temperature. This cause is also a function of temperature and time. A further cause of oil deterioration is the production of cinders of gasoline combustion. The production of cinders per unit of gasoline combustion contaminates oil; the amount of cinder per unit of gasoline combustion depends on engine conditions. Due to the recent advances in electronic fuel injection systems which reduce incomplete combustion and minimize cinder production, it is appropriate to consider that the amount of cinder production is simply proportional to the amount of total gasoline combustion. This total gasoline combustion is monitored by the RPM of the engine, oil temperature, and the engine running time. Monitored RPM can be converted as explained hereinafter.
Oil deterioration rate is also changed by driving conditions. For example, if an automobile is idling for a long period of time, driving faster than normal speed, or towing a heavy load, oil will deteriorate faster. These driving conditions are reflected in oil temperature. Monitoring oil temperature provides a reasonable basis for estimating oil deterioration due to such causes.
Besides the above mentioned causes, other factors can effect the rate of oil deterioration, such as air pollution and differences among oils and engines. The effect of these remaining factors, however, are not significant and have a secondary effect as compared with the previously mentioned major causes.
Consequently, engine oil temperature (or engine RPM), engine running time and elapsed time provide reasonable basis for estimating the degree of oil deterioration.